Gas burner system, gas burner and a method for combustion control

ABSTRACT

The invention relates to a gas burner system with at least one gas burner comprising: i) a mixing chamber (2) for supplying fuel gas and air; ii) a closed combustion chamber (3) located under the mixing chamber (2) and separated therefrom by a ceramic burner plate (16); iii) a jacket (30, 31) surrounding the combustion chamber (3) and heatable by radiation with an inlet (43) and an outlet (44) for liquid for heating, which jacket (30, 31) is provided with standing fire tubes (35) connecting onto the combustion chamber (3); iv) an outlet (46) for combustion gases; and v) combustion control means (17) situated in the combustion chamber (3) in the vicinity of the burner plate (16) which are connected to a control system. The invention relates further to a gas burner and to a method for controlling the combustion of a mixture of fuel gas and air in a combustion chamber which is provided with a ceramic burner plate, and a redox sensor with setting means for setting the temperature of the redox sensor, comprising: i) setting the redox sensor temperature T 1  which lies below the ignition temperature T o  of the mixture; ii) flushing the combustion chamber with air, iii) setting a redox sensor temperature T 2  which lies above T o  ; iv) supplying the mixture; and v) changing the supply of fuel gas and/or air subject to the generated redox sensor signal S.

The present invention relates to a gas burner, to a gas burner system inwhich such a gas burner is used and to a method for controlling thecombustion of a mixture for burning consisting of fuel gas and air.

By means of the present invention it is possible, depending on theprevailing conditions, that the ratio of fuel gas and air in the mixtureis controlled such that the quality of the combustion is optimal, i.e. aqualitative control on a low CO emission with a relatively low excess ofair (about 5 to 10%). An improved output is thereby realized with theformation of a relatively large amount of condensed water. The dischargeof NO_(x) is moreover reduced. Another important aspect of the inventionis that the invention can be applied with any type of fuel gas withoutadaptations of the gas burner or the system, and results in an optimal,almost complete combustion.

EP-A-154,361 describes a gas burner system in which combustion controlmeans, in the form of a redox sensor, are used for controlling thecombustion in a combustion chamber provided with a ceramic burner plate.A drawback to this system is that the sensor can be exposed over alonger period of time to reducing gases such as CO and CH₄, by which thesensor becomes poisoned. This system moreover has a configuration suchthat the heat transfer substantially takes place through convection. Thetemperature and the oxygen concentration in the vicinity of the sensorcan thereby fluctuate and thereby adversely affect the sensitivity andaccuracy of the sensor.

The present invention has for its object to provide a gas burner and agas burner system wherein in addition to the above-mentioned advantagesthe heat transfer takes place to considerable extent, i.e for more than50%, preferably more than 55% and more preferably 60% and more by meansof radiation.

In accordance with the invention this is achieved with a gas burnersystem according to the invention having at least one gas burneraccording to the invention, comprising:

i) a mixing chamber for supplied fuel gas and air;

ii) a closed combustion chamber located under the mixing chamber andseparated therefrom by a ceramic burner plate;

a jacket surrounding the combustion chamber and heatable by radiationwith an inlet and an outlet for liquid for heating, which jacket isprovided with standing fire tubes connecting onto the combustionchamber;

an outlet for combustion gases; and

combustion control means located in the vicinity of the burner plate inthe combustion chamber and connected to a control system.

The combustion control means preferably comprise a redox sensor, such asa Figaro Combustion Monitor Sensor, CMS 301 or 302 from FigaroEngineering Inc. This sensor comprises a sintered, metaloxide-comprising semiconductor material that substantially consists oftin dioxide.

This redox sensor preferably comprises at least one spiral filament andmeans with which the spiral filament can be adjusted to two differentglow temperatures. It is thus possible to control the operation of thegas burner at a temperature such that explosions are avoided in the caseof the presence of a combustible mixture and, after determining goodoperation at a higher glow temperature and allowing a combustiblemixture to be supplied, the combustion is started.

Since the heat transfer takes place to a considerable extent by means ofradiation, the surface heated by radiation can be enlarged if morepreferably the standing fire tubes are curved sideways in the jacket.

The system and the gas burner can be protected against irregularcombustion or cessation of the combustion by connection of a mg sensorto the combustion chamber.

The output of the system and the gas burner can be further increased byutilizing the temperature of the combustion gas leaving the fire tubesfor further generation of heat. It is therefore recommended that anindirect heat exchanger through which fire tubes pass is connected tothe water casing.

Another aspect of the invention relates to a control method forcombustion of a mixture of fuel gas and air for burning, wherein use ismade of a redox sensor. The operation of the gas burner can herein becontrolled when this method comprises:

setting the redox sensor temperature T₁ which lies below the ignitiontemperature T₀ of the mixture;

ii) flushing the combustion chamber with air;

iii) setting a redox sensor temperature T₂ which lies above T₀ ;

iv) supplying the mixture; and

v) changing the supply of fuel gas and/or air subject to the generatedredox sensor signal S.

During operation the quality of the combustion is preferably controlledby changing the amount of air in the mixture of fuel gas and air. Thisis preferably done in that in step v) the supply of air is reduced ifthe signal S approaches a minimum value S_(min), and in that in step v)the supply of air is increased if the signal S approaches a maximumvalue S_(max). Starting up the burner system takes place when after stepii), step iii) follows if the signal S falls from S₁ to S₂, and furtherwhen after step iii), step iv) follows if the signal S rises from S₂ toS₃, wherein S₃ is greater than S₁. The operating state for combustion isreached in that the supply of mixture is maintained if in step iv) thesignal S falls after reaching a value S_(max).

Mentioned and other features of the gas burner system, the gas burnerand the combustion method according to the invention will be describedhereinafter in more detail on the basis of an embodiment which is onlygiven by way of an example, while reference is made to the annexeddrawing.

In the drawing:

FIG. 1 shows a partially broken away, perspective view of a gas burneraccording to the invention;

FIG. 2 shows a section across the line II--II from FIG. 1;

FIG. 3 is a graphic depiction of the signal generated by the sensorduring the starting and operating situation;

FIG. 4 shows on a larger scale detail IV from FIG. 1;

FIG. 5 shows on a larger scale detail V from FIG. 1;

FIG. 6 shows a variant of the detail from FIG. 5;

FIG. 7 shows a variant of detail VII from FIG. 1; and

FIG. 8 shows a section along the line VIII--VIII from FIG. 7.

FIG. 1 shows a gas burner 1 according to the invention which, togetherwith a control system (not shown here), forms a gas burner systemaccording to the invention. This gas burner system can comprise one ormore gas burners 1 according to the invention and can for example beused for central heating and hot water provision. The gas burners 1according to the invention can herein be connected in parallel or intandem.

The gas burner 1 according to the invention comprises a mixing chamber2, a combustion chamber 3 and a heat exchanger 4 which are arranged oneon the other.

A central heating unit placed in the attic and two hot water provisionsfor bathroom and kitchen each provided with a gas burner 1 according tothe invention can also be controlled with one control system.

The mixing chamber 2 is provided with an inlet 5 onto which connects ahanging pipe 7 open at the underside 6. Debouching into the pipe 7 inthe vicinity of the bottom end 6 is a nozzle 8 with which fuel gas 11can be supplied via a feed conduit 9 and a controllable valve 10, whenthe valve 10 is opened. The valve 10 is operated via a control line 12which is connected to the control system (not shown).

Further accommodated in the pipe 7 is an axial fan 13 whereof thedelivery side is directed toward the mixing chamber 2, and which isconnected to the control system via the control lines 14.

Further arranged in the mixing chamber 2 is a copper mixing gauze 15 tostimulate the mixing of fuel gas and air and to prevent flame blow-backfrom the combustion chamber 3 into the mixing chamber 2. A uniformpressure distribution is moreover furthered over the surface of aceramic burner plate 16 which separates the mixing chamber 2 from thecombustion chamber 3. For example a Tennaglo T (trademark) can be usedas ceramic burner plate.

Combustion control means 17 comprising a redox sensor 18 is arranged inthe substantially cylindrical combustion chamber at a short distancefrom the burner plate 16. The distance to the plate 16 is preferably 2to 5 mm.

The sensor 18 is shown in more detail in FIG. 5. The sensor 18 (FigaroCMS-202) comprises a sensor part 19 in which is arranged sintered SnO₂mixed with catalyst. This sensor part 19 is sensitive to changes in theconcentration of reducing gases at a temperature of 400°-1100° C.

The sensor 18 further comprises a spiral filament 20 arranged betweenterminals 21 and 22. These terminals 21 and 22 are joined to a controlunit 23 with which the spiral filament 20 can be set to two differenttemperatures T₁ and T₂. The control unit 23 is in turn connected via acontrol line 24 to the control system.

FIG. 6 shows a variant of the sensor 18. In this case the sensor 25 hasa spiral filament 26 disposed between the terminals 21 and 22 which iswound round the sensor part 19. The terminals 21 and 22 are againconnected to the control unit 23, while the terminals 27 and 28 of thesensor 25 are directly joined to the control system.

The cylindrical combustion chamber 3 is bounded at the sides and at thebottom by a lowered bottom part 29 of a cylindrical first jacket part 30which forms with another cylindrical jacket part 31 the jacket of theheat exchanger 4. The jacket parts 30 and 31 are joined at anoverlapping seam 32. The mixing chamber 2 is fixed to and rests on abottom edge 33, wherein the ceramic burner plate 16 rests in a profilering 34.

Debouching into the bottom part 29 is a large number of fire tubes 35which pass through the water casing 77 filled with water 36. The firetubes have a sideways bending portion 37. The combustion chamber is thusprovided with a maximum surface area heated by radiation which consistsof the standing edge 38, the bottom part 29 and the bent fire tubeportions 37.

As shown in FIG. 2, heat radiation which enters the fire tube 35 via aninlet 39 will not reach its outlet 40 because it will first encounterthe bent portion 37 of the fire tube.

The fire tubes 35 are fixed at one side in the bottom part 29 and at theother side to a collar 41 of a bottom part 42 of the jacket part 31.

Water to be heated flows in via an inlet 43 and leaves the heatexchanger 4 via an outlet 44 lying at a high level.

The fire tubes 35 debouch into a combustion gas chamber 45 onto whichdebouches an outlet 46 for combustion gas. At the lowest point of asloping bottom 47 of the combustion gas chamber 45 is an outlet 48 forcondensed water that drips out of the fire tubes 35 into the combustiongas chamber 45.

FIG. 4 shows a measuring sensor 49 according to the invention. Thesensor 49 comprises a NiCr/NiAl thermocouple 50 which extends through atube part 51 into the combustion chamber to a point close to the burnerplate 16. The presence of a flame on the burner plate 16 during startingup and during operation is detected with the measuring sensor 49. Thesignal from the measuring sensor 49 is transmitted through the controllines 55, 56 to a control unit 23 which is in turn connected via acontrol line 57 to the control system.

Instead of a separate measuring sensor 49 the measuring sensor can beintegrated into the sensor 18 as shown in FIGS. 5 and 6.

The combustion method which can be performed with the gas burner 1according to the invention will be elucidated in more detail hereinbelowwith reference to FIG. 3 wherein the signal S generated by the sensor isshown as a function of time t for a start-up period 58 and an operatingperiod 59.

At start-up the valve 10 is closed and the fan 13 is switched off. Attime t₁ the sensor 25 is heated with the spiral filament 26 by thecontrol system via the control unit 23 to a redox sensor temperature T₁(for example 400° C.). The sensor 25 will generate a signal S₁. The fan13 is started at time t₂. Ambient air 60 flows in, whereby thetemperature of the sensor falls, the signal therefrom falling to S₂,unless fuel gas is supplied as a result of a leaking valve 10 or as aresult of a mixture still present in the mixing chamber 2. This wouldproduce an increase in the signal S which would cause the control systemto decide to discontinue the start-up procedure.

After a flushing period, the sensor 25 will at t₃ be brought with thespiral filament 26 to a higher temperature t₂ (800°-1000° C.), atemperature at which a mixture for combustion will ignite. Due to thishigher temperature the sensor will generate a signal S₃ greater than S₂and greater than S₁.

The gas valve 10 will subsequently be opened at t₄, whereafter themixture of fuel gas and air will flow via the burner plate into thecombustion chamber and will be ignited by the hot sensor 25/spiralfilament 26. The sensor signal will increase and at t₅ the heating ofthe spiral filament 26 will be interrupted, whereby the start-up period58 is concluded.

As a result of the combustion the concentration of reducing gas in thecombustion chamber 3 will decrease and thereby also the signal S fromthe sensor.

The supply of air will for example be reduced from t₆ to an air excessof n=1.05, wherein a maximum of 50 ppm CO and 16 ppm NO_(x) occurs inthe flue gas that will leave the outlet 46.

When the air excess is further lowered by either reducing the speed ofrevolution of the fan 13 or by increasing the supply of gas via thevalve 10, the signal S will increase. When the signal S approaches amaximum value S_(max), or exceeds it (corresponding to about 30 ppm CO),the air excess will be enlarged, for example by increasing the speed ofrevolution of the fan 13 at t₇. The signal S will once again decreaseand when it approaches an S_(min) (for example 20 ppm CO) the speed ofrevolution of the fan 13 will be decreased at t₈ until it is increasedat t₉. It will be apparent that in this operating situation thecombustion is optimally regulated within narrow limits for the COconcentration in the combustion gas. When the heating requirement comesto an end, the gas valve 10 is then closed at t₁₀ and the fan 13 isstopped when the signal from the sensor reaches a zero value.

FIGS. 7 and 8 show a variant of a gas burner 61 according to theinvention wherein a second heat exchanger 62 connects to the heatexchanger 4. The second heat exchanger 62 comprises a cylindricalhousing 63 with exchanger pipes 64 which are provided at their top endwith a collar 65 of a top part 66 in which the coupling with acorresponding fire tube 35 takes place. Between the exchanger pipes 64are arranged partitions 67 whereby air 69 for feeding in via an inlet 68passes through the heat exchanger 62 via a labyrinth and, heated on thepipes 64 and the partitions 67, leaves the heat exchanger 62 via theoutlet 70.

FIG. 7 shows clearly that the second heat exchanger 62 is arrangedbetween the heat exchanger 4 and the combustion gas chamber 45.

The second heat exchanger 62 can be added later to the gas burner 1,without adaptations to the control and protection being necessary. Thehigher resistance created in the gas burner 1 by mounting the heatexchanger 62 does have an affect on the output of the fan 13, but thisis automatically brought to the correct value again via the sensorcontrol.

It will be apparent from the above that the gas burner system and thegas burner according to the invention can be used for burning a greatvariety of fuel gases with optimum output and with a minimal emission ofharmful combustion products such as CO, NO_(x) and hydrocarbons. Thecontrol and protection of the burner are good and inexpensive. The gasburner and the gas burner system are easy to maintain and less sensitiveto varying chimney draught, pollution and ageing.

Finally, it is possible to record the energy consumption of the systemor the gas burner by recording the switching operations carried out bythe control system.

I claim:
 1. A gas burner system with at least one gas burnercomprising:i) i) a mixing chamber for supplied fuel gas and air; ii) aclosed combustion chamber located under the mixing chamber and separatedtherefrom by a ceramic burner plate; iii) a jacket surrounding thecombustion chamber and heatable by radiation with an inlet and an outletfor liquid for heating, which jacket is provided with standing firetubes connecting onto the combustion chamber; iv) an outlet forcombustion gases; and v) combustion control means situated in thecombustion chamber in the vicinity of the burner plate which isconnected to a control system.
 2. The system as claimed in claim 1,wherein the combustion control means is a redox sensor.
 3. The system asclaimed in claim 2, wherein the redox sensor includes at least onespiral filament and adjustment means for adjusting the spiral filamentto two different temperatures.
 4. The system as claimed in claim 1,wherein the standing fire tubes are bent sideways in the jacket.
 5. Thesystem as claimed in claim 1, further including a sensor connected tothe combustion chamber.
 6. The system as claimed in claim 1, furtherincluding an indirect heat exchanger, through which fire tubes pass,connected to a water casing.
 7. A method for controlling the combustionof a mixture of fuel gas and air in a combustion chamber which isprovided with a ceramic burner plate, and a redox sensor with settingmeans for setting the temperature of the redox sensor, said methodcomprising the steps of:i) setting a first redox sensor temperature T₁below the ignition temperature T₀ of the mixture; ii) flushing thecombustion chamber with air; iii) setting a second redox sensortemperature T₂ above T₀ ; iv) supplying the mixture; and v) changing thesupply of fuel gas and/or air subject to the generated redox sensorsignal S.
 8. The method as claimed in claim 7, wherein in step v) thesupply of air is reduced when the signal S approaches a minimum valueS_(min).
 9. The method as claimed in claim 8, wherein in step v) thesupply of air is increased when the signal S approaches a maximum valueS_(max).
 10. The method as claimed in claim 7, wherein after step ii),step iii) follows when the signal S falls from S₁ to S₂.
 11. The methodas claimed in claim 7, wherein after step iii), step iv) follows whenthe signal S rises from S₂ to S₃, wherein S₃ is greater than S₁.
 12. Themethod as claimed in claim 7, wherein the supply of mixture ismaintained if in step iv) the signal S falls after reaching a valueS_(max).